DE2825009A1 - COATED CARBIDE BODY AND METHOD FOR ITS MANUFACTURING - Google Patents

Description

SANDVIK AKTIEBOLAG, Fack, S-811 01 Sandviken, Sweden

Coated hard metal body and process for its manufacture.

The invention relates to sintered hard metal body with thin and extremely wear-resistant surface layers are coated. The invention also relates to a method for producing such coated bodies.

It is known that the wear resistance of pressed and sintered Carbide bodies, such as inserts for machining, through the application of hard surface layers can be increased considerably. In particular, coatings made of metal carbides, metal nitrides or metal oxides are considered thin Layers (for example with a thickness between 1 and 2Ομΐη) has been applied to the hard metal core or the substrate. It is also known that in certain cases further advantages are achieved can be done by applying a thin coating that consists of two or more different layers that are on top of each other are upset. In particular, the use of a

ch carbide or a nitride as an intermediate layer under an outer one

Ceramic layer can be mentioned. Aluminum oxide (Al ₂ O.,) and zirconium

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oxide (ZrO ₂ ) are examples of such ceramic layers. A main method for applying the surface layers is the CVD technique (Chemical Vapor Deposition), in which the coating is deposited on a hot substrate by reaction between gaseous components. For the production of aluminum oxide layers, the most widely used CVD process so far is the one in which aluminum chloride is reduced by hydrogen, the aluminum chloride either being evaporated directly or being formed by the reaction between aluminum metal and chlorine or hydrogen chloride, and the reaction with water vapor takes place, which is either vaporized immediately or is formed by the reaction between hydrogen and carbon dioxide or oxygen.

Suitable hard, polycrystalline, compact and well-adhering coatings of aluminum oxide which have the desired wear-resistant properties have normally only been achieved at deposition temperatures above about 95O ° C. At lower deposition temperatures, loose and powdery deposits are usually obtained which consist of the gamma modification and / or the theta modification of aluminum oxide. At deposition temperatures of about 100O ⁰ C and above, the aluminum oxide phase, which has been normally detected, and it has been found for the coating of tools for suitable alpha-modification. However, this modification of the aluminum oxide is a high-temperature phase, which is normally not in the pure state by CVD processes during a deposition

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temperature below 100 ° C is generated. The stability of the Alumina deposited at temperatures below 100 ° C is dependent on the presence of impurities or Additives that either originate from the substrate to be coated or originate from the gas phase. When pure alpha alumina substrates are used, epitaxial growth of alpha alumina occurs by chemical vapor deposition only at deposit temperatures above about 1500 ° C.

This clearly shows that the risk of obtaining multiphase aluminum oxide coatings is considerable if one uses temperatures that are normally used in the manufacture of coated tools. In a multiphase Coating form the boundary areas between the various phases areas of considerable mechanical weakness, and they can therefore be the reason for premature tool errors.

The deposition of an aluminum oxide coating causes diffusion of different grades from the substrate and / or the gas phase. The interaction of the various diffusion, nucleation and growth mechanisms that lead to the formation of the coating control is very critical and can easily lead to the formation of inhomogeneous deposits. Because such mechanisms are often difficult to control a method by which a stable, distinct aluminum oxide phase can be produced would be extremely advantageous, as carbide bodies with a single-phase aluminum oxide coating are likely to have a better and more uniform finish

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compared to multiphase alumina coatings.

According to the present invention, it has now been found possible to manufacture a hard metal body with a Alumina coating is provided, which consists of a very interesting phase in terms of machining. The alumina, which is essentially single phase, consists of the kappa modification and it is its processing taken according to certain well known steps or guidelines. The layer can be coated on and also are applied to non-coated hard metal substrates, and it can also be used as surface or intermediate layers in multilayer coatings of various kinds will. The coating is preferably applied to an intermediate layer of a wear-resistant carbide, nitride or carbonitride and / or borides applied. Specifically, these are carbides, carbonitrides, nitrides and borides with any of the following elements formed: Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Si and B (with the exception of the boride formed with the element B). Carbides, nitrides and / or carbonitrides of titanium are particularly suitable as intermediate layers.

The coating or the hard metal body according to the invention can be processed by doping the aluminum oxide coating with a specific and controlled amount of substantially tetravalent titanium and / or zirconium and / or Hafnium ions during the deposition process, so that only

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borrowed or almost exclusively formed kappa alumina will.

The titanium and / or the zirconium and / or the hafnium can be introduced into the aluminum oxide coating with the aid of the Addition of a titanium, zirconium or hafnium halide, in particular from titanium tetrachloride, to the normal gas mixture used for the deposition of alumina. The addition from titanium halide to said normal gas mixture for co-deposition of aluminum oxide and titanium oxide is earlier been used to make composite alpha alumina / titanium sesquioxide (TipO_) to produce coatings. The present However, the invention relates to the precise determination of the amount of halide that must be added to the deposition gas mixture, so that titanium and / or zirconium and / or hafnium ions can be incorporated into the aluminum oxide, in such a way, that this leads to a comparison with the usual qualities of aluminum oxide coatings results in the most unexpected exclusive or almost exclusive formation of kappa alumina. If titanium and / or zirconium and / or hafnium are in the correct concentration and the correct valence state in the reactor environment is present, some (+4) or all of it is incorporated into the coating and causes the formation of the kappa modification.

The explanation is theoretically complex and does not need to be clarified, however it can be mentioned that in said earlier known process the titanium was probably added as trivalent ions

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which led to the formation of common alpha alumina Has.

The starting conditions are also of great importance for the invention the alumina deposition process, which changes the oxidation state of the surface of the substrate or the intermediate layer determine. In the case of an intermediate layer of, for example, titanium carbide, it has been found that oxidizing conditions before the alumina deposition process begins, there is no kappa phase of the alumina, but the alpha phase instead of the alumina.

A pre-oxidation of a titanium carbide intermediate layer before coating with alumina has already been suggested in the literature. The titanium oxide obtained in this way can either be more or less will dissolve from the underlying titanium carbide layer and form an oxycarbide, or it may from the aluminum oxide layer dissolve and form a mixed oxide. In the case of oxygen migration into the titanium carbide layer the oxicarbide because of the considerable amount of non-stoichiometry of titanium carbide and the mutual solubility of titanium oxide and titanium carbide.

Most surprisingly, it has been found that a Be

layering is made of kappa aluminum oxide

better than such

from the alpha modification, although the latter is more dense

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(3.99 kg / dm ³ compared to 3.25 kg / dm ³ for the kappa phase). One possible explanation is that this occurs either due to the observed finer grain size of the kappa phase or due to the improved bonding that occurs between the kappa aluminum oxide layer and the substrate, eg a titanium carbide layer. Improved bonding is expected on the basis that when kappa alumina is obtained using the invention, there will be no excessive amounts of titanium oxide on or in the top of the titanium carbide layer. The formation of titanium oxide causes an expansion in volume with respect to the underlying titanium carbide and this can have adverse effects on the adhesion in the surface area of the titanium carbide.

In the commercially available, double-coated (aluminum oxide-titanium carbide) Grades of cemented carbide also form considerable amounts of kappa aluminum oxide, and in fact two to 98% The surface is made up of kappa aluminum oxide, while the rest is made up of alpha aluminum. The scatter in the amount of So kappa alumina can be substantial in this case. Also, the size of the circular areas is alpha alumina quite large, namely 10 to 2ΟΟμΐη. When big Parts of the surface are made up of the alpha phase, the circular spots often merge with each other, resulting in irregular shaped areas of kappa aluminum oxide. Large areas of overlap of alpha alumina are undesirable because they can easily break open and be moved away by the chip or workpiece if they are in the critical areas of the

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Tool edge.

It has now been found that with the aid of the invention it is possible to reduce the amount of alpha alumina to less than 15%, and preferably less than 10%, in a consistent manner, as well as the size of the remaining alpha phases - to reduce stains to less than about 10μπι, preferably less than Siim .

The relationship between the size and the amount or area of the alpha phase spots has been shown in a diagram (Fig. 1). In previously known alumina coatings, as previously stated, - relatively large alpha phase spots and large changes in the size of the alpha phase spots and also the amount of alpha phase can be observed. The lower limit of this range is marked in the diagram by the curve DE. According to the invention, it has now been found possible to achieve greatly improved properties if the size and occurrence of the alpha-phase spots are set so that they are in the area AOB, preferably in the area A ¹ OB ¹ , fall as shown in FIG.

Another advantage of the invention is the increased speed the deposit, which leads to drastically reduced production times. Depending on the added amounts of halides growth rates are achieved which those achieved without the addition of halide by a factor of

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exceed two or more. Apart from an increase in the production speed of coatings as such the increase in the growth rate is of direct advantage for the quality of the coating, namely in so far as than this reduces the length of time the coating is at high temperatures, thereby reducing the likelihood of undesired changes in the structure of the coating due to the applied high temperature is considerably reduced will.

The aluminum oxide layer can be formed by any conventional method are deposited, but preferably by the CVD process with the addition of a titanium and / or zirconium and / or hafnium dopant. This can also be used when the hard metal substrate is coated with an intermediate layer or when several successive layers are to be applied before or after the actual aluminum oxide layer. The chemical vapor deposition of the kappa aluminum oxide layer can separate from the deposition of the interlayer (or other possible surface layers), but it should preferably be subsequently be made in the same device, so that a control over the oxidation of the surface the intermediate layer can be achieved. Excessive oxidation of the surface should be prevented because oxidation, e.g. a titanium carbide surface causes a volume expansion and a change in structure that result in a loss of adhesion can lead.

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The thickness of the aluminum oxide layer is usually 0.1 to 2Ομΐη, often 0.2 to 1Ομπι, but in particular 0.3 to 3μπι. However, the applied oxide layer is preferably 0.5 to 2μΐη thick. The thickness of the intermediate layer or the following layers, which are above or below the aluminum coating, is usually the same size, i.e. 0.1 to 2Ομΐη. By doing Case that intermediate layers of wear-resistant carbides, nitrides, carbonitrides and / or borides are used the thickness normally 1 to 8μπι and preferably 1.4 to 7μΐη.

For the deposition of the kappa aluminum oxide coating, that can System can be used in which a hydrogen reduction of an aluminum halide, preferably the chloride (AlCl-), and the Reaction with water vapor or oxygen is applied. The aluminum halide can be produced in gas form, namely either by evaporation of the solid or liquid form, or by reaction of aluminum metal with chlorine gas or hydrogen chloride. The water vapor can be generated in gaseous form by evaporation or, preferably, by the reaction between hydrogen and carbon dioxide. Titanium tetrachloride (TiCl.) For the doping The alumina is produced in vapor form by evaporation of the liquid. When other halides of titanium, zirconium or the hafnium are used, the steam can be generated in a similar manner. The reaction products are in the reaction chamber out, in which the sintered hard metal samples to be coated lie. The samples can either be immediate be heated by induction heating or indirectly by heating a support plate or the reactor, e.g. with the help of the

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electrical resistance heating. The deposition temperature can range from 700 ° C to 1200 ° C. But it is preferably in the range of 95O ° C to 1150 ° C, being the actual temperature depends on the type of impurities contained in the dopants used.

The concentrations of aluminum chloride and water vapor (or hydrocarbon or oxygen) in the reacting gas mixture should preferably be approximately stoichiometric. In the case of chemical vapor deposition, the concentration of the tetravalent halide or halides should be in the range of 0.03 to 0.5%. It should preferably be less than 0.2% of the total amount of gas that is fed to the reactor. If the deposition is performed by any means other than chemical vapor deposition, an appropriate amount of halide or halides should be used. It is also important that the concentrations of CO _{2 and H 2 are} carefully controlled. The recommended amounts of tetravalent halides apply to near stoichiometric proportions of carbon dioxide and aluminum chloride. In the case of more reducing conditions in the reactor, the lower ratios of carbon dioxide-to-hydrogen or steam-to-hydrogen require that a larger amount of tetravalent halides be added. The total pressure of the gas phase can be in the range from 1 to 760 torr, but preferably from 30 to 80 torr. If the deposit is not carefully controlled according to the conditions outlined above, alpha or other undesirable alumina phases will become

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formed in considerable quantities.

It has also been found that an addition of titanium and / or Zirconium and / or hafnium dopants significantly increases the rate of deposition of the alumina. As an example for the results obtained are shown in Fig. 2, a diagram which the growth rate as a function of the amount of added titanium tfretrachloride (in percent by volume) shows. From the Diagram can be calculated that, for example, an addition of about 0.05% titanium feetrachloride to a three-fold increase in Growth rate (from 0.1 | i, m / h to about Ο, 3μΐη / 1ι) out Has.

The kappa alumina coating usually contains one certain amount of titanium, hafnium and / or zirconium, which are in the oxide layer in the form of, for example, titanium dioxide, hafnium dioxide or zirconia. The addition of Ti, Hf and / or Zr has the formation of the oxide during the aluminum oxide coating influenced. In cases where titanium dioxide is part of the layer, the amount is usually 0.5 to 10%.

The following example illustrates various conditions that are necessary for the production of surface-coated cemented carbide bodies in accordance with of the invention and the results obtained in examining such bodies.

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2825QQ9

example 1

A number of ISO quality sintered carbide cutting inserts M2O were with a 6μπι thick layer of titanium carbide coated and then subsequently with a 1 μm thick layer Kappa aluminum oxide coated.

The kappa alumina deposition conditions were as follows:

Reactive gas mixture: H

AlCl-

CO ₂

TiCl ^

CO

90 1 % 7 kPa) 2 9 % K) 6th % 0, % 1, % 2 5 m / s 50 Torr (6, 1010 ⁰ C (1283 1, hours

Speed of gas flow:

Gas mixture pressure:

Temperature:

Deposit time:

The kappa alumina coating was completely dense, polycrystalline and adheres well. In a study of the performance of inserts coated according to the invention showed an increase in the life of the insert up to 20% compared with the life of inserts that had been coated by the known method, in which

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no tetravalent halides were added is.

Example 2

There were «. A number of hard metal cutting inserts in the same Coated as in Example 1, with the exception that the coating consists of an intermediate layer of 3tun titanium carbide and an outer layer of 3μΐη consisted of aluminum oxide. the Deposition time for the alumina was increased to 5 hours while the time for carbide deposition was halved while the deposition conditions were the same as in Example 1.

The outer coating was made of kappa phase alumina to the extent of 99%, while the remainder consists of alpha-alumina in the form of round areas with a diameter of no more existed as 5μπι.

In a comparative test of the performance of these coatings, which was carried out in the same manner as that of Example 1, an increase in the life of the inserts by found about 100%.

Example 3

A number of hard metal inserts with ISO quality M 20 were placed directly on the hard metal substrate with Kappa aluminum

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oxide coated. The conditions were the same as in the example 1 applied for the oxide coating. In this case too, the life of the inserts was extended up to about 20% compared to inserts coated with alumina according to the previously known technique. The investigations were carried out by turning steel with a carbon content of about 1%.

Example 4

There were sintered hard metal bodies with an intermediate layer of 2μΐη hafnium nitride and a surface layer of 1μΐη kappa aluminum oxide coated. The two layers were applied by CVD deposition, with the intermediate layer following the normal Practice was applied while the surface layer was applied according to the following process conditions.

Reactive gas mixture:

Speed of gas flow

Pressure of gas mixture temperature

Deposit time

H ₂

AlCl,

CO ₂

ZrCl ^

CO

89 05 ^% 2 95 % 7th 5 % ο, c ¥> 1, C. ^% 2, m / s 55 Torr 1015 ° 1 hour

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A layer of well adhering aluminum oxide was obtained, which consisted of at least 90 ° kappa phase.

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Claims (1)

DIPL.-ING. KLAUÖ BEHN DIPL.-PHYS. ROBERT MÜNZHUBER PATENT LAWYERS WIDENMAYERSTRASSE 6 D-8000 MUNICH 22 TEL. (089) 22 25 30 - 29 51 92 6.6.1978 Our reference: A 108 78 Be / De PATENT CLAIMS 1. A hard metal body which contains at least one carbide in addition to a binding metal, and to which at least one thin, wear-resistant surface layer is applied, which consists essentially of aluminum oxide, characterized in that the aluminum oxide consists of at least 85% of the kappa modification and that the rest, which essentially forms the alpha modification, is designed as surface parts or spots with a size of at most 1Ομπι, the size and occurrence of the surface parts are set so that they are in the area AOB, preferably in the area A ¹ OB ¹ , of the diagram according to FIG. 1 lie. 2. Hard metal body according to claim 1, characterized in that the thickness of the aluminum oxide layer 0.1 to 20μΐη, preferably 0.3 to 3μΐη. 3. hard metal body according to claim 1 or 2, characterized in that that between the aluminum oxide layer and the hard metal body, a thin intermediate layer is applied, which is made of wear- Bankhaus Merck, Finck & Co .. Munich, (BLZ 7OO3O4OO) Account no. 254649 Bankhaus H. Aufhäuser. Munich, No. 261300 Post check: Munich 2OQ04-800 Telegram address: patent senior 809850/1034 OFWGINAL INSPECT «© 282b009 solid carbide, nitride, carbonitride and / or boride, preferably of the elements Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Si and / or B. 4. hard metal body according to claim 3, characterized in that the thickness of the intermediate layer 1 to 8μΐη, preferably 1, 5 to 7μπι, amounts to. 5. hard metal body according to claim 3 or 4, characterized in that that the intermediate layer consists of titanium carbide, titanium nitride and / or titanium carbonitride. 6. hard metal body according to one of claims 1 to 5, characterized in that that the aluminum oxide layer contains additions of titanium, zirconium and / or hafnium. 7. A method for producing a hard metal body according to a a
of claims 1 to 6, in which a halide or more halides of aluminum-containing gas acts at high temperature on the hard metal body, characterized in that the gas has a doping addition of tetravalent titanium, zirconium and / or hafnium ions in an amount of preferably 0.03 to 0.5% of the total amount of gas supplied is added. 809850 / 103A